High Voltage Electron Microscopy and its Application in Biology

• Published in: Philosophical transactions of the Royal Society of London. Series B, Biological sciences Biological sciences, 1971-05, Vol.261 (837), p.35-44
• Main Author: Cosslett, V. E.
• Format: Article
• Language: English
• Subjects: Electric potential; Electron microscopes; Electron microscopy; Electrons; Image resolution; Imaging; Materials; Microscopes; Microscopy; New Developments in Instrumentation; Radiation damage
• ISSN: 0962-8436; 0080-4622; 1471-2970; 2054-0280
• DOI: 10.1098/rstb.1971.0034

The advantages and limitations of electron microscopy at voltages up to 1 MV are outlined. Greater thickness of specimen can be examined, the increase being almost linear with applied voltage for carbonaceous material. Alternatively, a much improved image resolution is obtained from a specimen of given thickness. For such a specimen, radiation damage and temperature rise is less than at 100 kV, but these effects probably set a limit to the maximum thickness of specimen which can be examined at 1 MV. The main disadvantage is that contrast decreases with increasing voltage, as also does the response of the fluorescent screen and of photographic emulsions. The prospective slight gain in ultimate resolving power, which might make possible the imaging of atoms, is largely offset by difficulties in maintaining electrical and mechanical stability. Examples are shown of the usefulness of high voltage microscopy for examining whole chromosomes and thick sections (up to 2 $\mu m$). Stereomicrography is necessary if the three-dimensional structure of such relatively thick specimens is to be properly evaluated. The further possibilities for investigating wet samples in special environmental cells are outlined. It is concluded that the prospects for observing living material are remote.